The present invention relates to a receiver circuit for a push-pull transmission method.
The basic mode of operation of such a push-pull transmission method is explained briefly below with reference to FIGS. 1 and 2.
FIG. 1 schematically shows a push-pull transmission arrangement having a transmission device 1, a first and second channel 2, 3 and a receiver device 4. The basic principle of such an arrangement consists in generating two complementary transmission signals Sout1, Sout2 from a two-value transmission signal Sin to be transmitted, which is fed to the transmission device 1, transmitting said transmission signals Sout1, Sout2 via the two separate channels 2, 3 and, in the receiver circuit 4, reconstructing the transmission signal from the signals Sin1, Sin2, that are available at the outputs of the channels 2, 3.
The transmission channels 2, 3 may be realized in arbitrary fashion and may, in particular, in each case comprise a transformer for potential decoupling of transmitter 1 and receiver 4. The illustration of suitable driver circuits for converting the complementary transmitter output signals Sout1, Sout2 to levels suitable for transmission, and of suitable demodulator circuits for converting the signals present at the channel outputs to levels suitable for processing by the receiver 4 has been dispensed with in the figure for reasons of clarity.
In order to transmit a two-value input signal Sin by means of a push-pull method via channels with potential barriers such as transformers, for example, it is known to convert a rising edge of the input signal Sin into a pulse on one of the two channels and a falling edge of the input signal Sin into a pulse on the other of the two channels, so that, during the transmission of such a two-value input signal Sin, pulses are never transmitted simultaneously on both channels. This is utilized for filtering at interference signals since it can be assumed that pulses that are received simultaneously on both channels are attributable to common-mode interference signals. The receiver circuit 4 must be designed to the effect that, in the event of simultaneous detection of reception signals on both channels, it ignores these signals, so that these signals have no effect on the output signal Sout.
FIG. 2 shows by way of example the signal profile in the case of such a push-pull transmission method. FIG. 2 shows the input signal Sin and the signals Sin1, Sin2 resulting from said input signal Sin at the channel outputs. In the example, an interference pulse is superposed on the channel output signals Sin1, Sin2, which interference pulse occurs simultaneously on both channels and is therefore filtered out in the reception circuit 4.
In principle, the circuit components of the push-pull transmission path must enable interference and useful signals to be distinguished unequivocally and ignore interference signals, in which case the transmission speed should be as high as possible, that is to say that the signal propagation times in the individual circuit components should be as low as possible, and the transmission arrangement should be able to be realized as cost-effectively as possible.
Difficulties in the suppression of interference signals can occur when interference signals which occur simultaneously on the two channels have differences in amplitude, so that the interference signal on one of the channels lies above a detection threshold and the interference signal on the other channel lies below a detection threshold, as a result of which a useful signal transmission is assumed incorrectly at the receiver end. Problems can also arise when the interference signals on the two channels occur with a slight temporal offset with respect to one another.
It is an aim of the present invention to provide a receiver arrangement for a push-pull transmission method which is robust with respect to the interference signals that occur during the signal transmission and which can additionally be realized simply and cost-effectively.